Induced Aromaticity and Electron-Count Rules for Bipyramidal and Sandwich Complexes of s- and d-Metals

Structures and stability of an extended series of bipyramidal, sandwich and sandwich-bipyramidal mixed complexes formed by conjugated cyclic hydrocarbons (CH) n with s-(Li, Na, K, Be, Mg, Ca) and d-(Cr, Mn, Fe) metals have been studied using DFT B3LYP/6-311+G(df,p) calculations.Stable structures of the compounds satisfy a general (6n + 6d + 12c) electron-count rule, where n stands for total number of the basal hydrocarbon rings, d is total number of d-metal centers (or separate sandwich moieties) and is total number of apical metal-carbonyl groups.It is shown that stabilization of the studied polyhedral organometallic structures (induced aromaticity) is caused by filling 6 -electronic shells of basal (4-6)-membered cycles provided by donation of additional electrons from metal centers thereby acquiring closed 18electron shells.